Card retainer devices are used in “separable thermal-mechanical interfaces”, or STMI's. Such STMI's are often used in ruggedized computer assemblies used in demanding environments, such as military and aerospace vehicles. The assemblies are composed of a chassis, electronics card modules and card retainers. The chassis is made with guiding features to accept several card modules, which are inserted and “plugged-in” to backplane electrical connectors. Card retainers are mounted on each card module and clamp the card into the chassis guides when actuated. Adoption of these assemblies has been widespread due to the inherent ease of maintenance and open architecture that encourages upgrades to systems as they become available. For the most part, these computer assemblies have been standardized by the VMEBus International Trade Association (VITA) which has developed rules and guidelines for the manufacture of chasses, cards and card retainers to ensure that products from industry vendors can successfully integrate to provide flexible computing solutions to developers.
Thermal management of the computer assemblies is currently approached in several ways. For very low power assemblies, no active thermal management is needed. However, due to the high density packaging and the enclosed air volume that the chassis creates, cooling by natural convection is limited. For higher power assemblies, forced air convection is used in which fans and vents are placed in the chassis walls to flow ambient air through the assembly, cooling the electronics by forced convection. This approach can be effective but is limited to applications which are low altitude, low ambient temperature and in non-contaminating environments. For the most demanding applications, the chassis is completely sealed, and the cards are designed to have higher in-plane thermal conductivity. Heat is conducted from the card mounted electronics to the STMI, where the card retainer clamps the card tab into the chassis guide. Heat is conducted through this interface to the chassis walls, which are externally cooled either by forced convection of air or by forced convection in the form of a coolant jacket. In applications where the enclosure is externally cooled, the thermal connection formed by the card retainer is a significant thermal resistance.
In recent years, computing requirements have become more demanding due to the focus on network-centric warfare, with the increased use of graphics, video, digital signal processing, sensor data acquisition and other computer-intensive tasks. As a result, computational power has increased and has generated challenging thermal management issues within standardized enclosures. Thus, to enable higher computational power, while maintaining component operating temperatures, efforts are needed to reduce thermal resistance.
One card retainer currently used to clamp is the wedge lock which has found acceptance in industry and is used in a large number of applications. The device achieves the desired card clamping force to retain the card in the chassis rails by actuating a series of trapezoidal “wedges”. These wedges are hollowed and sit axially in a row along a threaded fastener and/or a guide. When the threaded fastener is turned, it advances the end wedge, and force is applied to the wedge interfaces causing outward motion of the wedges. The wedge lock is primarily designed as a clamp and enables card-to-chassis heat transfer by forcing the card and chassis faces into intimate contact. Since it was designed this way, the device itself is not made to be very thermally conductive.
Another known card retainer is the cardlock clamp shown in U.S. Pat. No. 8,743,544. The cardlock clamp is also a wedge-type device in which a pair of actuating bolts compresses a stack of wedges to provide outward wedge motion. The wedges are cut at compounded angles, allowing the retainer to expand in two directions. Unlike the previously mentioned wedge lock device, the wedges of the cardlock clamp do not make direct contact with the card and chassis themselves but are nested inside two L-shaped brackets which thermally connect the card and chassis. The thermal connection of the card and chassis enhances the thermal performance of the device by utilizing more of surface area to transfer heat. This helps lower heat flux by opening more paths for heat rejection from the conduction card to the chassis.
Despite the improvement in thermal performance, the cardlock clamp shown in U.S. Pat. No. 8,743,544 has shortcomings that limit its use. For example, the cardlock clamp achieves the aforementioned thermal enhancements by exerting force onto the side-walls of the chassis. Unfortunately, the chasses have not been designed to accept loading and can experience undesirable deflection, and possibly permanent deformation, when forces are applied.
It would, therefore, be beneficial to provide a card retainer device which provides for sufficient thermal transfer between a card module and a chassis while reducing or minimizing the forces applied to the chassis walls. It would also be beneficial to provide a card retainer device in which actuation may be achieved while only having access to a single side of the device.